Here's a quick step by step guide for running an ssh server.

1. $ apk add openssh — install the ssh tools and the ssh server.
2. $ ssh-keygen -A — create the host keys.
3. $ passwd — Set a password for root to protect your iOS device
4. $ echo 'PermitRootLogin yes' >> /etc/ssh/sshd_config
5. $ /usr/sbin/sshd

You should now be able to ssh to your device with username root and the password you typed.

If you are trying to connect via ssh from the same device, make sure you set the port configuration of sshd to use a non standard one (greater than 1024, eg: 22000).

You can do this by editing /etc/ssh/sshd_config and set Port 22000 (Replace 22000 with any non-standard port).

After this, you can ssh (from iSH itself) using ssh root@localhost -p 22000

The simplest way to set this up is to let ssh do it for you, this saves you the hassle of fiddling with a remote config file, ensuring everything has the right permission, and so on.

This assumes the destination device allows logins with password, in order to transfer the pubkey. If this is not the case you have to transfer the pubkey the traditional way.

Use the same parameters as you use for a normal ssh session, but replace the word ssh with ssh-copy-id. Using the above example this would be ssh-copy-id root@localhost -p 22000

When you run this, you will still need to supply the password one last time. After this has completed, you are now able to login without providing the password for the remote account. And you can disable password logins in your sshd server.

To login as root without a password, I follow the usual steps to create a key with ssh-keygen and ssh-copy-id the public key to the phone. But when I attempt to login, I am still prompted for password. Permission of .ssh dir is 700, and permission of authorized_keys is 600.

On the iPhone I stop the sshd server:

service sshd stop

And restart in debug mode:

/usr/sbin/sshd -d -p 22

Now the ssh server on the phone is listening and will log activity to the screen. I open another terminal window and ssh to the phone as root. I am prompted for the password, but do not enter it yet. Over in the debug output I see the following message:

trying public key file /root/.ssh/authorized_keys

Authentication refused: bad ownership or modes for directory /root

I enter the password, and am logged into the phone as root. I change the ownership like this:

chown root /root

chown root /root/.ssh

And logout. Now when I ssh to the phone as root, I am logged in successfully with the key, and not prompted for a password.

Additionally, if sshd returns an error about the root user account being locked, you can set a dummy password hash on the account to "unlock" it:

echo "root:*" | chpasswd -e